HTTP/2 (originally named HTTP/2.0) is a major revision of the HTTP network protocol used by the World Wide Web. It was derived from the earlier experimental SPDY protocol, originally developed by Google.
HTTP/2 was developed by the Hypertext Transfer Protocol working group httpbis (where bis means “second”) of the Internet Engineering Task Force (IETF).
What is a Protocol?
A protocol is a set of rules that govern the data communication mechanisms between clients (for example web browsers used by internet users to request information) and servers (the machines containing the requested information).
Protocols usually consist of three main parts: Header, Payload, and Footer.
The Header placed before the Payload contains information such as source and destination address as well as other details (such as size and type) regarding the Payload.
The Payload is the actual information transmitted using the protocol.
The Footer follows the Payload and works as a control field to route client-server requests to the intended recipients along with the Header to ensure the Payload data is transmitted free of errors.
The system is similar to the postal mail service. The letter (Payload) is inserted into an envelope (Header) with destination address written on it and sealed with glue and postage stamp (Footer) before it is dispatched.
What is SPDY?
SPDY (pronounced SPeeDY) is a networking protocol developed by Google with the purpose of speeding up the delivery of web content. It does this by modifying HTTP traffic which in turn reduces web page latency and improves web security.
HTTP, while powerful in its day, cannot keep up with the demands of today’s digital world, which is the reason SPDY was introduced to help meet those demands.
What is HTTP/2?
HTTP/2 is the second major version update to the HTTP protocol since HTTP1.1 which was released more than 15 years ago. The HTTP/2 protocol was developed due to the ever-evolving digital world and the need to load more resource intensive web pages.
SPDY was also implemented to help reduce web page latency users experience when using HTTP1.1. HTTP/2 is based off SPDY, however, contains key improvements that have led to the deprecation of SPDY in February 2015.
How does HTTP/2 work?
Whenever you click on a link to visit a site a request is made to the server. The server answers with a status message (header) and a file list for that website. After viewing that list, the browser asks for the files one at a time. The difference between HTTP 1.1 and HTTP/2 lies in what happens next.
Say you want a new LEGO set. First, you go to the store to buy your LEGO. When you get home, you open the box and look at the instructions, which tell you what you have to do: one brick at a time. So for every brick, you have to look at the instructions to see which brick to use next. The same for the next brick, and so on. This back-and-forth keeps happening until you have finished the entire LEGO set. If your set has 3,300 bricks, that’ll take quite a while. This is HTTP1.1.
With HTTP/2 this change. You go to the store to pick up your box. Open it, find the instructions and you can ask for all the bricks used on one section of the LEGO set. You can keep asking the instructions for more bricks, without having to look at the manual. “These bricks go together, so here they are.” If you want it really quickly, you could even get all the bricks at once so you can build the set in an instant.
Differences from HTTP1.1
Similar to SPDY, using HTTP/2 does not require any changes to how web applications currently work, however, applications are able to take advantage of the optimization features to increase page load speed.
Differences between the HTTP1.1. and HTTP/2 protocol includes the following:
- HTTP/2 is binary, instead of textual
- It is fully multiplexed, instead of ordered and blocking
- It can use one connection for parallelism
- It uses header compression to reduce overhead
- It allows servers to “push” responses proactively into client caches instead of waiting for a new request for each resource.
Is it HTTP/2.0 or HTTP/2?
The Working Group decided to drop the minor version (“.0”) because it has caused a lot of confusion in HTTP/1.x.
In other words, the HTTP version only indicates wire compatibility, not feature sets or “marketing.”
Similarities with HTTP1.x and SPDY
| HTTP1.x | SPDY | HTTP2 |
|---|---|---|
| SSL not required but recommended. | SSL required. | SSL not required but recommended. |
| Slow encryption. | Fast encryption. | Even faster encryption. |
| One client-server request per TCP connection. | Multiple client-server requests per TCP connection. Occurs on a single host at a time. | Multi-host multiplexing. Occurs on multiple hosts at a single instant. |
| No header compression. | Header compression introduced. | Header compression using improved algorithms that improve performance as well as security. |
| No stream prioritization. | Stream prioritization introduced. | Improved stream prioritization mechanisms used. |
Conclusion
HTTP/2 is without a doubt the direction the web is moving towards in terms of the networking protocol that is able to handle the resource needs of today’s websites. While SPDY was a great step forward in improving HTTP1.1, HTTP/2 has since further improved the HTTP protocol that has served the web for many years.
According to W3Techs, as of November 2018, 31% of the top 10 million websites supported HTTP/2.
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